Developmental differences in the composition of lens proteins have been observed with monkey and human lenses. These alterations in composition were similar to those observed in rodent lenses at similar stages in development. In order to investigate the role in which these changes may affect optical clarity, the lens cystallin proteins as well as the glycoproteins from the membrane of the lens cells have been studied. Differences in the crystallin composition may give an indication of factors involved in congenital cataracts. Changes in individual crystallins may also be important to understand the aging process in the lens. Beta- and Gamma- crystallin compositions are changing in the early embryonic period of the primate lens. The Beta-crystallins have much higher apparent molecular weights in the fetal lens perhaps indicative of a different organization of the subunits of these proteins during this stage of development. In addition, the main Gamma-crystallin in the embryonic lens is only a very minor component in the adult lens. As the lens cells differentiate into fiber cells, the glycoprotein composition on their membranes changes. Specific glycoprotein differences have been seen in cataractous rodent lenses compared with normal lens; and using lectins, primate lenses can now be probed for changes related to cataract formation and development.